Inflatable eight-corner reflector



Sept. 10, 1963 INFLATABLE EIGHT-CORNER REFLECTOR Filed May 19, 1959EQDIO WAVE REFLECTIVE SHEET INVENTORS THOMFIS EDWARD HoRAcE GRAY JAMESJones-mwrow HTTOIQNE Y T. E. H GRAY ETAL 3,103,662

United States Patent Company Limited, London County, England, a Britishcompany Filed May 19, 1959, Ser. No. 814,290 Claims priority,application Great Britain June 3, 1958 5 Claims. (Cl. 343-18) Thisinvention relates to reflector devices for radio waves, and especiallysuch devices used for radar purposes. The invention is concerned withsuch devices incorporating corner reflectors, comprising three plainreflective surfaces set mutually perpendicular to each other so as todefine the internal corner angle of a cube. Such a reflector has theproperty of reflecting along a path parallel to their incident pathwaves striking any of its surfaces from any direction within the solidangle defined by the surfaces. In particular the invention is concernedwith a device incorporating a reflector comprising eight cornerreflectors with their apices coincident, as defined by both sides ofthree plane sheets intersecting each other at right angles. Such areflector, which will be termed an octonary reflector, will reflectwaves incident from any direction along a path parallel to theirincident path. If each reflective surface of an octonary reflector is aright-angled triangle, the straight base edges of the triangularsurfaces define the edges of an octohedron. For convenience such areflector will be referred to herein as an octahedral reflector. If thetriangles are isosceles the octahedron is regular.

It has been proposed to construct an octonary reflector of flexibleradio wave-reflective sheet material which can easily be folded andpacked for storage or when not required 'for use. These flexiblereflectors must, however, be provided with some means for holding thesheets taut when in the erect position so that the reflective surfacesare all truly flat and correctly disposed in relation to each other.Rigid supporting members are not entirely convenient owing to storagedifliculties and, if they are collapsible, the time that may be taken toerect them.

It has been proposed to mount an octonary reflector inside an inflatablespherical balloon of material permeable to radio waves by connecting theends of the lines of intersection of the surfaces (the apices in thecase of an octahedral reflector) to the internal surface of the balloon.This is a diflicult assembly since the parts must be secured togetherwhen the balloon is in its deflated condition, and if the connectionpoints are not correctly positioned in the balloon, or if it expandsunevenly on inflation, puckering of the reflective surfaces may result.Furthermore, if the balloon is to be made of material of lowextensibility it is diflicult to construct the assembly with the desiredaccuracy owing to the problem of making a spherical or near-sphericalballoon from essentially flat material.

According to the invention a reflector device for radio waves comprisesan octonary reflector formed from flexible radio wave-reflective sheetmaterial enclosed within and secured by its edges to an inflatableenvelope of flexible material permeable to radio waves, of dimensionssuch that on inflation of the envelope the sheets of the reflector areheld taut and in the desired relation to each other.

Since the edges of the reflector are secured to the envelope, the sheetsof the reflector are not only pulled outwardly on inflation but theedges are themselves firmly held, restraining any tendency of the sheetsto pucker.

The reflector and its envelope may be of any desired shape, but arepreferably symmetrical.

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One embodiment of the invention is illustrated by way of example by theaccompanying drawings in which:

FIGURE 1 is a perspective view of a regular octahedral reflector of theprior art.

FIGURE 2 is a perspective view of the reflector of our inventionenclosed in its envelope and inflated in condition of use.

The reflector shown in FIGURE 1 is assembled from twelve identicalsheets 1 of flexible radio wave-reflective material of right-angledisosceles triangular shape, secured together along their side edges 2with their right-angled apices coinciding, so that their base edges 3,when the sheets 1 are all held taut and flat, define the edges of aregular octahedron.

The sheets 1 may be textile fabric, such as nylon mesh, with a metalliccoating such as silver. Alternatively they may be formed from metalfoil. They may be secured together along their edges 2 by any convenientmeans, for example by stitching or by adhesive. Preferably, however, theradio wave-reflective material is laminated to flexible plastic sheetfor reinforcing it, and if the plastic is a thermoplastic the sheets 1can be secured together by heat sealing.

The reflector shown in FIGURE 1, after assembly, is enclosed within anenvelope of flexible radio wave-permeable material as shown in FIGURE 2.In this figure the envelope is shown in its inflated condition, in whichit is substantially in the shape of a regular octahedron.

The envelope is assembled around the reflector from eight identicalsheets 4 of the radio wave-permeable material, each of equilateraltriangular shape with edges 5 of length equal to the edges 3 of thereflector. The sheets 4 are secured together and to the correspondingedges 3 of the reflector by these edges 5 so as to form a closedenvelope which when inflated will be of the desired shape. One of thesheets 4 has an inflation valve 6 as shown, and some or all of thesheets of the reflector have openings for admitting inflating gas to allthe compartments defined within the envelope by the reflector.Conveniently the tip of each corner 7 of the reflector may be cut offbefore assembling the envelope so as toprovide these openings.

On inflation the envelope is distended to its substantially octahedralshape, erecting the reflector and holding it in its position of use withthe sheets 1 in the desired mutually perpendicular relation. Althoughthe sheets 4 of the envelope may tend to belly out when inflated, sothat the shape is not truly octahedral, the seams between the edges 5and 3 Will remain straight so that the reflector sheets 1 are restrainedfrom puckering.

The envelope sheets 4 may be formed from any flexible gas-imperviousmaterial which is permeable to radio waves, and they may be securedtogether and to the reflector along their edges by any convenient meansproviding a gas-tight joint. Preferably, however, they are formed fromtextile fabric of a long chain polymeric amide such as nylon impregnatedwith a plastic such as polyvinyl chloride or other thermoplastic whichprovides the desirable properties of toughness with low extensibility sothat their distortion on inflation is small, and which can be securedtogether by heat sealing. When the reflector sheets also incorporate athermoplastic as mentioned above, this provides a very strong seam.

With this embodiment, only two shapes of sheet are involved, theisosceles triangular reflective sheets 1 and the equilateral triangularsheets 4 of the envelope, so providing for simplicity and economy inmanufacture.

Any convenient inflating gas may be used, depending upon the uses towhich the reflector device is to be put.

0 For example, air or hydrogen may be used.

The invention provides a reflector device which can be erected quicklyand simply by inflation and requires no other supports for holding itsreflective surfaces in the desired relation. Furthermore, it can bestored easily and compactly. It is particularly suitable for use on lifeboats and life rafts, especially inflatable life rafts in which meansmay be provided for inflating the reflection device at the same time asthe raft.

Having now described our invention what we claim is:

1. A radar reflector device for radio waves comprising sheets of radiowave-reflective sheet material lying in three planes which intersecteach other at right angles to define eight corner reflectors havingcoincident inner apices, six outer apices and eight edges of the radiowave-reflective sheet material each of which edges extends between anadjacent pair of said outer apices, and an inflatable envelope offlexible material permeable to radio waves having at least eightoutstanding edges, the outstanding edges extending in said planes ofradio wave-reflective sheet material and the corner reflectors beingenclosed within said envelope and secured to said outstanding edgesthereof by their edges.

2. A reflector device according to claim 1 wherein the envelopecomprises a plurality of sheets of the flexible radio wave-permeablematerial.

3. A reflector device according to claim 1 wherein the envelope wheninflated is substantially in the shape of a regular octahedron havingthe same edge lengths as the edges of the radio Wave reflective sheets.

4. A reflector device according to claim 3 wherein the envelope has asingle inflation valve, and the radio wave-reflective sheets haveopenings for admitting inflating gas to all the compartments definedbetween them and the envelope.

5. A reflector device according to claim 3 wherein the envelope isthermoplastic.

References Cited in the file of this patent UNITED STATES PATENTS

1. A RADAR REFLECTOR DEVICE FOR RADIO WAVES COMPRISING SHEETS OF RADIO WAVE-REFLECTIVE SHEET MATERIAL LYING IN THREE PLANES WHICH INTERSECT EACH OTHER AT RIGHT ANGLES TO DEFINE EIGHT CORNER REFLECTORS HAVING COINCIDENT INNER APICES, SIX OUTER APICES AND EIGHT EDGES OF THE RADIO WAVE-REFLECTIVE SHEET MATERIAL EACH OF WHICH EDGES EXTENDS BETWEEN AN ADJACENT PAIR OF SAID OUTER APICES, AND AN INFLATABLE ENVELOPE OF FLEXIBLE MATERIAL PERMEABLE TO RADIO WAVES HAVING AT LEAST EIGHT OUTSTANDING EDGES, THE OUTSTANDING EDGES EXTENDING IN SAID PLANES TO RADIO WAVE-REFLECTIVE SHEET MATERIAL AND THE CORNER REFLECTORS BEING ENCLOSED WITHIN SAID ENVELOPE AND SECURED TO SAID OUTSTANDING EDGES THEREOF BY THEIR EDGES., 